Caulking your fixed windows not only protects the frames from water damage, it also makes your house more comfortable by keeping the elements outside. It's best to use silicone caulk because it is waterproof and remains flexible after it has cured — but silicone is more difficult to apply than other types of caulk. It is sticky, and although some solvents can soften it, none can dissolve it, so there is a potential for a mess unless you work carefully. Properly prepare the tube, handle the caulking gun correctly and cleanly finish each bead, and the job will go smoothly.
Cut the plastic tip of the caulk tube at a 45-degree angle with a utility knife. The tip is tapered, and cutting it too close to the tube will result in more material emerging at one time than you can handle. For most jobs, the hole should be about 1/8 inch in diameter, which means cutting very close to the small end. The angled cut will help you direct the flow where you want it.
Puncture the tube seal by inserting a 16d nail into the tip and pushing on it. Remove the nail, then pull the plunger of a caulking gun all the way back and insert the tube. Pump the trigger a few times until the plunger contacts the bottom of the tube and material begins to emerge from the tip, then push the pressure-relief knob located near the trigger to stop the caulk from flowing.
Start caulking the window at any corner and position yourself so you are pulling the gun toward you as you caulk. Don't push the gun toward fresh caulk. The caulk will collect around the tip and eventually leave a large deposit that you'll have to clean up.
Hold the gun at an angle so that the tip is almost touching the gap between the window and the framing and keep the gun moving while you pull the trigger. The cut on the tube tip should be facing downward. Adjust the speed at which you move the gun so that the material that emerges fills the gap with as little excess as possible.
Depress the pressure-relief knob whenever you stop; try to reach the opposite corner of the window in one application. Pull the gun away from the window and cover the tip with a rag. Even after you release pressure, a small amount of caulk will continue to emerge.
Run your finger along the fresh bead to smooth it and make a concave surface. Clean the excess from your finger frequently with a moistened rag. If you've applied the right amount of caulk, there won't be much excess.
Caulk the other three sides of the window in the same way.
Things You Will Need
Be sure to clean the gap thoroughly before you caulk it. Silicone caulk doesn't adhere well to dust, paint chips or old caulk.
Silicone caulk gives off a strong odor that resembles vinegar. If you're sensitive to such odors, wear a respirator while working indoors.